Modern appliances such as electric fans, other AC motors, LEDs, and other DC powered devices work best when supply power is controlled to optimize parameters such as power factor, phase differences and voltage differences. See for example US No. 20140125266 (Huynh et al.), which teaches a processor-controlled high and low side driver circuitry such as for driving inductive loads. Huynh discloses a combination of low and high voltage dies in a power management multi-chip module (PMMCM) containing two dies for driving a fan, as shown in FIG. 1 which is a reproduction of Huynh's FIG. 2 used for explaining this prior art reference.
One die contains a pulse-width modulator (PWM) and other components that include low-side drivers. The second die contains the ultra-high voltage high-side drivers that supply drive signals to the external high-side transistors. External low-side transistors are driven directly by low-side drivers of the first die. For example FIG. 2, which is the prior art of Huynh's FIG. 5, shows a circuit diagram of one low-side driver 233, and one high-side driver 236 of the power management integrated circuit (PMIC) die 108. Low-side driver 233, coupled to a +12 volt supply voltage VP, controls external discrete NFET 260 via terminal LSI 264. High-side driver 236, also coupled to a +12 volt supply voltage VP, has P-channel and N-channel FETs 323 and 324 that are interconnected as a complementary logic inverter that supplies an output to the gate of external discrete NFET 272.
Block 332 is digital logic that supplies a control signal to turn on and off the external discrete NFET 272. Block 333 is a level shift circuit that receives the digital logic control signal and shifts the signal so that it is output as a digital logic control signal 335 onto input lead 336 of high-side driver 236.
Such power modules benefit from component selection and circuit optimization for lowered manufacturing complexity/costs and higher power consumption efficiency.
Power control circuits that run such appliances typically contain a microprocessor that has to be powered up upon turning on the appliance. To achieve this, normally an alternating power high voltage is rectified and a low voltage applied to a Vcc power pin in series with a start resistor and in parallel with a capacitor. The microprocessor in turn often generates a reference voltage such as 5.0 volts for use in associated control circuitry. Outside the microprocessor is typically found a voltage or current regulator necessary to operate the microprocessor within a suitable voltage range.
Further regarding PFC circuits, the use of a MOSFET as the switch component in the PFC gives a turn-on that can be at a low voltage, which favorably reduces PFC switching losses. The PFC typically can operate in a current-mode control or a voltage-mode control. A boost converter is often used in PFC circuits that can operate in different modes, such as a continuous conduction mode (CCM), a discontinuous conduction mode (DCM), and a critical conduction (or boundary or borderline conduction) mode (CrM or BCM).
The fundamental states of operation (power switch ON and power switch OFF) can be demonstrated by considering, for example, the CrM PFC converter operating mode, with a diode bridge output to a parallel capacitance and series inductance. When the power switch is turned on, this circuit produces a linearly rise or increase in the coil current, Icoil. When turned off, this produces a linearly decrease in the coil current Icoil. The resulting current waveform in the two operating states in a critical mode conduction PFC shows a coil current peak. At another point, the core is reset. This relationship between when the reset occurs is the basis of the voltage-mode control of the PFC converter operating in the critical conduction mode, CrM
A problem of power control circuits arises when a microprocessor needs initial power supplied via a Vcc pin in parallel with a capacitor, and when other circuits also need typically higher power to start. When all circuits start at the same time, the microprocessor cannot begin to work until a later time when a suitably high voltage is obtained. This delays overall circuit operation because the microprocessor has to regulate and control the other circuits, while at the same time waiting to start control while the other circuits are competing for power up current. The additional power demands put pressure on designing a larger Vcc capacitor, with commensurate decrease in board space, increased cost and increased start up time needed to charge up the capacitor to a suitable voltage.
An example of circuits used in this field is shown in U.S. No. 20140177284 (Nakano). FIG. 3 is a copy of Nakano's FIG. 1 for explaining this circuit. FIG. 3 summarizes how this reference teaches the use of a constant current limited circuit needed between a rectified power supply and a microprocessor power input. FIG. 3 is a switching power supply apparatus circuit and the broken line shows a start circuit. The circuit has a capacitor C1, a starting circuit 1a, and a transformer T with primary, secondary and tertiary windings P1, S1, P2 respectively, a MOSFET switching element Q10. Resistor R10 detects the current flowing through switching element Q10 and a control circuit 3 controls the on-off switching of Q10. Capacitors C10, C11 and diodes D10, D11 make up rectifying and smoothing circuits. In some cases an analog power supply IC is used for power in the start up circuit, which adds further expense and complexity. Accordingly one problem in this field is the need for a more efficient start up power system that can minimize board space, cost, complexity and start up time.